Method for Bending Thermoplastic Pipes

Abstract

A method for producing a bent pipe from thermoplastic material with end cross-sections, central points of which have in relation to one another a positional tolerance on the basis of LN xy/JAR xy/FAR xy in relation to one another. A straight pipe element is introduced into a tool and a portion of the straight pipe element is heated that is located in the bending region to a temperature which lies above a glass transition temperature of the thermoplastic material by a first temperature value. The straight pipe element is bent about the heated bending region of the tool by a freely selectable bending angle, which has a spatial alignment in an XYZ system of coordinates that is fixed with respect to the pipe. The pipe is then cooled below the glass transition temperature by a second temperature value.

1 . A method for producing a bent pipe from thermoplastic material, the bent pipe comprising end cross-sections, central points of which have in relation to one another a positional tolerance that is a maximum of +/−1 mm in relation to one another, the method comprising:
 a) introducing a straight pipe element into a tool, which is heated in a bending region; 
 b) heating a portion of the straight pipe element that is located in the bending region; 
 c) heating the bending region to a temperature which lies above the glass transition temperature of the thermoplastic material by a first temperature value; 
 d) bending the straight pipe element about the heated bending region of the tool by a bending radius that is ensured by the form of the tool by a freely selectable bending angle, which has a spatial alignment in an xyz system of coordinates that is fixed with respect to the pipe; and 
 e) cooling the pipe element bent after step d) below the glass transition temperature of the thermoplastic material by a second temperature value, 
 wherein the bent pipe further comprises: 
 straight portions and at least two bent portions, 
 wherein pairs of the straight portions span different planes, 
 wherein each bent portion has a bending radius and a bending angle, 
 wherein each bent portion has an ovality of less than 7% and a wall thickness which deviates from the straight portion by less than 10%, 
 wherein two of the straight portions each have a respective end cross-section with a central point, and 
 wherein the bent pipe material brings about a transition from brittle energy-elastic behavior to soft entropy elastic behavior subject to heating above glass transition temperature and bringing about a transition from soft entropy elastic behavior to brittle energy-elastic behavior when cooled below glass transition temperature. 
 
     
     
         2 . The method according to  claim 1 , wherein steps a) to e) are repeated at least once at a different location of the bent pipe and the spatial alignments of the bending angles are different. 
     
     
         3 . The method according to  claim 1 , wherein the first temperature value lies in a range from 5° to 100° C. 
     
     
         4 . The method according to  claim 1 , wherein the second temperature value lies in a range from 5° to 100° C. 
     
     
         5 . The method according to  claim 1 , wherein the heated bending region of the tool has an electrically heated flank, channels with temperature-controlled liquid, an infrared emitter, an induction device or a hot-air blower. 
     
     
         6 . The method according to  claim 1 , wherein the first and second temperature values ensure a tolerable temperature transition with minimal distortion of the bent portion of the bent pipe. 
     
     
         7 . The method according to  claim 1 , wherein a tolerance range of at most 0.5° is maintained for the bending angle. 
     
     
         8 . The method according to  claim 1 , wherein, after step e), the bending angle in the bent region still has a tolerance of 0.5°. 
     
     
         9 . The method according to  claim 1 , wherein cold air, liquefied gas, a cooled tool or water is used for cooling the bent pipe. 
     
     
         10 . The method according to  claim 1 , wherein the first and second temperature values and the bending radius are coordinated with one another, and the roundness of the pipe is maintained, the ovality being less than 5%. 
     
     
         11 . The method according to  claim 1 , wherein an inner side and an outer side of the bent pipe have a surface quality that is substantially the same. 
     
     
         12 . The method according to  claim 1 , wherein the thermoplastic material is polyether ether ketone, polyether sulphone, polyether ketone, polyphenylene sulphide or polyethyleneimine. 
     
     
         13 . The method according to  claim 1 , wherein, in step d), the bending region is supported from the inside by an auxiliary component. 
     
     
         14 . The method according to  claim 13 , wherein the auxiliary component is a mandrel, gas pressure or a heat-resistant scratchproof filling material, in particular glass or steel beads. 
     
     
         15 - 22 . (canceled)